Fluid ejection heads for fluid ejection devices such as ink jet printers, vapor evaporation devices, and the like continue to be improved as the technology for making the ejection heads continues to advance. New techniques are constantly being developed to provide low cost, highly reliable fluid ejection head structures that can be manufactured in high volume with high yield having relatively low amount of spoilage or ejection head damage.
In order to increase ejection head speed and volume output, larger ejection heads having an increased number of ejection actuators are being developed. However, as the ejection head size and number of ejection actuators increases, manufacturing apparatus and techniques are required to meet increased tolerance demands for such ejection heads. Slight variations in tolerances of parts may have a significant impact on the operation and yield of suitable ejection head products.
The primary components of the fluid ejection head are a substrate or chip containing fluid ejector actuators, and a nozzle plate attached to the chip. The chip is typically made of silicon and contains various passivation layers, conductive metal layers, resistive layers, insulative layers and protective layers deposited on a device surface thereof. For thermal fluid ejection heads, individual heaters are defined in the resistive layers and each heater resistor corresponds to a nozzle hole in the nozzle plate for heating and ejecting fluid from the ejection head toward a target media. Fluid ejection heads may also include bubble pump type ejection head. In a top-shooter type ejection head, nozzle plates are attached to the chips and there are fluid chambers and fluid feed channels for directing fluid to each of the heaters or bubble pumps on the chip either formed in the nozzle plate material or in a separate thick film layer. In a center feed design for a top-shooter type ejection head, fluid is supplied to the channels and chambers from a slot or via that is conventionally formed by chemically etching or grit blasting through the thickness of the chip. The chip containing the nozzle plate is typically bonded to a thermoplastic body using a heat curable adhesive to provide a fluid ejection head structure.
The thermal cure process locks the components together at an elevated temperature. The heater chip has a relatively low CTE (coefficient of thermal expansion) while the plastic body has a relatively high CTE. Heating the components causes each one to expand according to their respective CTEs. As the parts cool and shrink, the higher CTE plastic body shrinks more than the lower CTE silicon heater chip resulting in thermal stresses on the chip. The force-deflection (spring rate) characteristics of the chip and body determine the equilibrium deflection of each part. In many cases the plastic body spring rate dominates the chip spring rate causing via compression and nozzle plate bowing. Nozzle plate bowing may result in poor drop placement or nozzle plate structural failure.
In order to address the issues related to thermal compression of the chip as the chip and plastic body cool, ceramic substrates have been attached to the chip. However, ceramic substrates substantially increase the cost of the ejection head. Silicon bridges in a via area of the chip have also been used, but such silicon bridges result in fluid flow problems in the chip via area.
It is believed that a predominant contributor of chip distortion, cracking, and nozzle plate damage is the coefficient of thermal expansion mismatch between the chip and the thermoplastic body. During manufacturing, when the chip and body go through the adhesive cure cycle, chip distortion is introduced as the components cool. Accordingly, there continues to be a need for improved manufacturing processes and techniques which provide improved ejection head components and structures without product loss due to chip cracking or nozzle plate damage.
With regard to the above, there is provided a fluid ejection head assembly having improved assembly characteristics and methods of manufacturing a fluid ejection head assembly. The fluid ejection head includes a fluid supply body having at least one fluid supply port in a recessed area therein and a semiconductor chip attached in the recessed area of the fluid supply body adjacent the fluid supply port using a thermal cure adhesive. A compression prevention body having a coefficient of thermal expansion ranging from about 1.0 to less than about 30 microns/meter per ° C. disposed adjacent to the fluid supply port of the fluid supply body and the semiconductor chip.
In another embodiment, there is provided a method for reducing compressive forces on a semiconductor chip of a fluid ejection head during a thermal cure process for attaching the semiconductor chip to a fluid supply body. The method includes providing a fluid supply port in a recessed area of the fluid supply body. A compression prevention body is disposed adjacent to the fluid supply port of the fluid supply body and the semiconductor chip, wherein the compression prevention body has a coefficient of thermal expansion ranging from about 1.0 to less than about 30 microns/meter per ° C. A semiconductor chip is attached in the recessed area of the fluid supply body adjacent the fluid supply port using a thermal cure adhesive. The adhesive is thermally cured to fixedly attach the semiconductor chip in the recessed area of the fluid supply body.
In a further embodiment, there is provided a method for reducing via distortion in a semiconductor chip of a fluid ejection head during a thermal cure process for attaching the semiconductor chip to a fluid supply body. The method includes providing a fluid supply port in a recessed area of the fluid supply body. A spherical body is disposed adjacent to the fluid supply port of the fluid supply body and the semiconductor chip, wherein the spherical body has a coefficient of thermal expansion ranging from about 1.0 to less than about 30 microns/meter per ° C. A semiconductor chip is attached in the recessed area of the fluid supply body adjacent the fluid supply port using a thermal cure adhesive. The adhesive is thermally cured to fixedly attach the semiconductor chip in the recessed area of the fluid supply body.
In some embodiments, the compression prevention body has a shape selected from a sphere, a rectangular cube, and a cylinder. In one embodiment, the compression prevention body is a spherical body having a diameter ranging from about 2.0 to about 3.5 millimeters.
In some embodiments, the compression prevention body is made of a material selected from silicon, glass, alumina, stainless steel, or a low CTE polymeric material.
In some embodiments, the compression prevention body has a coefficient of thermal expansion of less than about half a coefficient of thermal expansion of the fluid supply body.
In some embodiments, the fluid ejection head assembly is a micro-fluid ejection head attached to a fluid supply body wherein the fluid ejection head assembly further includes a compression prevention body.
For the purposes of this disclosure, the term “fluid ejection head assembly” means, at least, a combination of cartridge body, compression prevention body, and semiconductor chip.
An advantage of the foregoing structures and methods is that after the adhesive is cured and the parts have cooled, the fluid supply body compresses on the compression prevention body and the chip simultaneously rather than only on the chip. Since the compression prevention body has a spring rate much greater than that of the semiconductor chip in the areas where the chip may be deflected, the deflection of the chip is significantly reduced so that compression of the via in the chip is reduced. Likewise, the compression of the nozzle plate attached to the chip will also be significantly reduced.